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The permeability properties of skeletal muscle from Periplaneta americana and Sphinx ligustri have been studied by several methods and in each the effects of pharmacological agents and of temperature have been investigated. The properties of the microsomal preparation of skeletal muscle were characterized. Compared with preparations from many other types of excitable cell, although probably not muscle, the microsomal preparation was a typical in lacking an enzyme synergistically stimulated by monovalent cations and in being insensitive to strophanthin G. Normal trans-membrane inorganic ion distributions of skeletal muscle were determined. The ratios were similar in the two animals and not markedly dissimilar from those of vertebrate muscle / blood ratios. The results obtained with Sphinx muscle differed from those of previous workers. Based on the results obtained a new saline was developed for bathing the muscles of Periplaneta and Sphinx which proved to be more suitable than salines used by other workers. Intra cellular microelectrode recordings were made from resting and active skeletal muscle of Periplaneta. The relative contributions to the resting membrane potential of actively and passively distributed ions were determined. A considerable hyperpolarizing contribution to the resting membrane potential was made by a metabolically dependent constant current generator. Similar results were obtained using Sphinx skeletal muscle. An electrical model was derived to account for the phenomena observed. The individual contributions of inorganic ions to depolarizing electrogenesis were determined. Sodium was found to make a major contribution. The possible role of electrogenic pumps i n the development of end-plate potentials was discussed. The excitatory postsynaptic potential of Periplaneta skeletal muscle was compared with the end-plate potential of vertebrate skeletal muscle and the possible nature of the biphasic response of Periplaneta muscle to excitation discussed. Possible mechanisms of excitatory and inhibitory eleotrogenesis were related to the model developed to describe the resting membrane potential.

The phenomenon of temperature adaptation, as measured by the mobility of the heat death point, was demonstrated in Aatacus pallipes Lereboullet. Analysis of muscle, haemolymph and environment during lethal high temperature exposure showed dramatic Na(^+) and K(^+) concentration changes in all three compartments. In all cases the monovalent cations showed a net movement down their respective electro-chemical gradients, although this was sometimes only observed after a brief initial period during which the ions tended to exhibit a net movement up their electro-chemical gradients. The results indicated that heat death occurred when the haemolymph K(^+) concentration rose to about 9 mM. No relationship between the haemolymph Na(^+) concentration and the heat death point was observed. Electrophysiological experiments indicated that lethal high temperatures caused an increase in the conductivity (-, permeability) of the sarcolemma following comparable exposure times to those causing heat death in the whole animal. The Mg(^++)activated ATPase (EC 3.6.1.3.) which is involved in the control of sarcolemmal permeability was shown to be inactivated by lethal high temperatures. It was therefore concluded that the increased sarcolemmal permeability was caused by the thermal inactivation of this enzyme. The spontaneous activity of the CNS was only slightly affected by exposure to lethal high temperatures. Raising the extracellular K* concentration to the levels observed in animals at the time of heat death caused a massive increase in nervous activity. The sarcolemmal Mg (^++) activated ATPase from warm adapted crayfish was shown to be more resistant to high temperatures than that from cold adapted crayfish. This could be correlated with the greater heat resistance of the sarcolemmal Mg(^++) activated ATPase and conductivity seen in the warm adapted animals. It is proposed that the primary lesion of heat death in Astacus pallipes Lereboullet is the thermal inactivation of the sarcolemmal Mg(^++) activated ATPase which allows muscle K(^+) to move into the haemolymph. The activity of the CNS is increased markedly by the high haemolymph K(^+) resulting in loss of coordination and death. The thermal sensitivity of the Mg(^++) activated ATPase is modified by the previous thermal history of the crayfish and is involved in the mechanism of temperature adaptation.

This thesis attempts to relate the structure and physiology of superposition compound eyes of mesopelagic and bathypelagic decapods to their visual environment. An anatomical survey at the light microscope level showed that bathypelagic decapods have stellate or hypertrophied rhabdoms and little or no proximal shielding pigments. In contrast, species found in upper mesopelagic depths have fusiform rhabdoms that are square in cross section in the dorsal region of the eye and often have stellate rhabdoms ventrally. Proximal shielding pigment was much more noticeable in mesopelagic species than in bathypelagic species. In addition, shielding pigments were only found distal to the basement membrane in mesopelagic species. Observation of eyeshine intensity distribution around the eye confirmed histological evidence that the reflective tapetum is restricted to ventral regions of the eye in mesopelagic species while bathypelagic species have a complete tapetum. Measurements of aperture diameters using green light and white light showed that they are significantly smaller under green light. Since most mesopelagic species will rarely encounter anything other than blue/green light, the functional aperture of most superposition eyes is probably less than has been estimated previously. Physiological evidence suggests that spectral sensitivity and the ability of the eye to respond to rapid changes in light intensity changes with light adaptation in coastal species. Deep-sea species appear unable to light adapt. It is suggested that one reason for this may be the limited ability of the rhabdomeral membrane to respond to the increased rate of ion cycling induced by elevated light levels. This, and previous evidence, may also explain the ease with which the eyes of deep-sea decapods become damaged upon exposure to relatively low light intensities. A ray-tracing model was formulated that predicted the sensitivity and acceptance angle for all the species examined histologically. This agreed well with previous empirical models and suggested that the dioptric layer focuses light from a point source onto the axial rhabdom. The model suggests that sensitivity to extended sources increases with depth. It is suggested that this is an associated (concomitant) rather than causal relationship and that the eyes of mesopelagic and deep-sea decapods are primarily designed to maximise sensitivity to `point' sources such as bioluminescent events.

The identification of five predicted proteins (dP2XA-E) with homology to vertebrate P2X receptors in Dictyostelium discoideum proved a unique opportunity to explore purinergic receptor function in a simple unicellular eukaryote from outside the animal kingdom. dP2XE was shown to be expressed as a trimer and trafficked to the cell surface in Xenopus oocytes. However, no currents were detected to extracellularly applied ligands. This lack of function was potentially due to inaccurate post-translational modifications since dP2XE expressed in oocytes and D. discoideum displayed different molecular weights. Unexpectedly for a potential ligand-gated ion channel, dP2XE-eGFP displayed a solely intracellular distribution in D. discoideum, localising to the endolysosomal and contractile vacuole systems. Ablation of the p2xE gene by homologous recombination revealed a role for dP2XE in axenic growth in suspension, associated with a modest defect in cytokinesis, and a potential involvement in the calcium signalling and homeostasis functions of the contractile vacuole. Both this distribution and disruption phenotype were mirrored for p2xA. The existence of purinergic signalling in D. discoideum was demonstrated by utilising an apoaequorin expressing strain to show that extracellular ATP and ADP evoked increases in intracellular Caˆ{2,+}. Indicative of P2X receptor activation, responses were rapid and transient, required extracellular Caˆ{2,+}, inhibited by Gdˆ{3,+}, modified by extracellular pH and remained unaffected by deletion of either the single heterotrimeric G\beta or iplA genes. ATP/ADP responses were unaffected by ablation of either the p2xA or p2xE genes leaving dP2XB-D as potential candidates. Inhibition of the large P2X-like response with Znˆ{2,+} revealed the presence of a much smaller response with a slower time course indicating that P2Y-like receptors may also be present. The work presented in this thesis demonstrates that D. discoideum possesses cell surface purinergic receptors for extracellular ATP/ADP and extends our knowledge of the intracellular role of purinergic signalling in this organism.

The published articles, p. 149 onwards, are not available in the electronic version of this thesis due to copyright restrictions. The full version can be consulted at the University of Leicester Library.

This thesis examines the ontogenetic development of the honey bee immune system in an ecological immunity context. I have optimised established immunological techniques to examine how aspects of the constitutive and induced innate immune response in the honey bee, Apis mellifera L., are affected by life-history and parasite infection. I have used three optimised immune assays to gain a measure of the timing and magnitude of specific immune effector systems in the honey bee, and explored the consequences of variation in immune efficacy throughout development and aging. The major findings of this thesis are: 1. Neither workers or drones employ phenoloxidase for immune defence in the pre-pupal stages 2. Sexual selection does not eliminate the need for an immune response in adult drones 3. In both sexes, there is an ontogenetic up-regulation in immune function with adult age 4. In the case of workers, this increase in immune response is not linked to age polyethism, but rather a continuous increase in investment beginning immediately after adult eclosion 5. Immune challenge results in a decrease in phenoloxidase activity, and an increase in antimicrobial peptide production in adults 6. The antimicrobial peptide immune response shows signs of senescence in immune challenged adult workers and drones 7. Colony investment in immune responses acts on a temporal scale and responds positively to an increased threat of parasitism 8. Parasitism produces variation in colony defence strategies 9. Rainfall is an important factor in the successful establishment of an infestation by the varroa mite, varroa destructor, in honey bees.

A group of five giant fibres. (40 - 6ojx in diameter) occurs in both oesophageal connectives of Caroinus maenas (L.) and similarly in three other species of crab investigated. Four of these fibres react to visual and tactile stimuli in a phasic numner. They seem to be subjected to excitatory and inhibitory control. The fifth fibre has input from the oontralateral statocyst and fires on head up and same side down rotations round the horizontal axes. It alao fires on forced leg movements upwards about the basal joints, summing input from both sides. There are four other directional statocyst fibres in each connective Carcinus responding to rotation round the vertical axis, or to rotation round both horizontal axes. Two of these also have input from the legs. One of these is supplied by the contralateral statocyst and three by the ipselateral one. The detailed structure of the brain of Carcinus is as reported in Bethe (1897) and Bullock and Horridge (1965) except that the antennary and tegumentary neuropiles have been confused by both authors, and the accessory lobe is present (contrary to Bullock and Horridge). The giant fibres all have contralateral cell bodies in the dorsal anterior medial cells. The main branches are in the dorsal deuterocerebrm with a few branches in visual neuropiles of the protocerebrum. All five fibres have an ipsilateral branch with processes in the antennary and Documentary neuropiles which join the main axon where the connective merges into the brain. The detailed anatomy of the connective is similar to the crab leg motor nerve (Horridge and Chapman,1964) only the sheaths round large fibres are thinner withea less well developed inner sheath. There are 2300 fibre in the connective of Carcinus. Approximately 45 of these have diameters greater than 10 jj. Most of the fibres are between 1 and 5 P- diameter. Other interneurons investigated have cell bodies in the posterior cells and ipsilateral dendrites. One other large fibre (40 u iiameter) responded to visual and taotile stimuli and had a oontralateral oell body. This fibre could be pieced with the giant fibres. No additional inputs to any fibres investigated vras revealed in free walking animals with implanted electrodes. No direct effect was apparent on stimulation of these fibresroalthough electrical stimulation of isrtain others both in the connective and optic tract yielded a variety of complicated ordered appendage movements including the full swimming reflex. Swimming is also elicited by head, down rotation of the animal and is activated by sensory information from the statocyst eyes and legs. It is suggested that the visual and tactile giant fibres form a group more similar to giant fibres in the cockroach and locust than in i the crayfish. It is further suggested that the giant statocyst fibre is involved in back leg movements which stabilize the crab during the rearing reflex and also may provide phasio information of integrated leg and body position during walking.